Publication DE102010015256 relates to a method for manufacturing an airbag case comprising a chute channel, a case and a net comprising a step of folding the net and a step of maintaining the folds of the net by the intermediary of an assembly element before the manufacturing of the flap and of the chute channel. The folded portion is intended to subsequently form a hinge between the flap and the chute channel. These types of manufacturing methods are already used and provide satisfaction. However, with a concern for reducing the risk of injury to the occupants of the vehicle while still reducing the number of manufacturing steps and the manufacturing time of these safety devices, this invention has objectives to improve this.